Method and device for guiding a web of material

ABSTRACT

The present invention relates to a method for guiding a flat web of material ( 1 ) in which the web of material ( 1 ) runs in an arrangement of rotating rollers at a web speed v F . The web of material is guided in its peripheral region via a spreader roll ( 2 ) which produces a tensile stress in the transverse direction, i.e. crosswise relative to the machine direction of the web of material ( 1 ), wherein this tension in the transverse direction is controlled by means of closed-loop control of the circumferential speed v R  of the spreader roll ( 2 ) and/or by open-loop control of the cant angle α and/or of the wrap angle β between the surface of the spreader roll ( 3 ) and the web of material ( 1 ) and wherein the circumferential speed v R  is greater than the web speed v F .

FIELD OF THE INVENTION

The present invention relates to a method and a device for guiding a webof material (1) which is guided and transported between rotatingrollers.

BACKGROUND OF THE INVENTION

In the production and the processing of flat webs of material these websare guided and transported between rotating rollers. In order totransport the web a certain level of tension is produced in thelongitudinal direction of the web of material. Due to this tension inthe direction of travel, folds or shifts arise in the longitudinaldirection which are undesired and which later produce lateralelongations in the reel which may result in the material beingcompletely unusable. Accordingly, it is necessary to smooth andstraighten the folds and shifts in the running web of material broughtabout by the tensile stress in the longitudinal direction by means oftensile forces in the crosswise direction.

Devices for spreading webs of material are known in the state of theart. US 22 89 196 describes what is referred to as the banana roller.This cylindrical roller is composed at least on the surface of anelastomeric material and is specially shaped. The roller is curved overits entire length and is pressed against the running web of material.When the roller is pressed into the running web of material, the shapeof the roller causes spreading in the transverse direction. However, thetransmission of force by transverse forces that can thus be generatedand the transverse movement achievable in this case is extremely smalland, therefore, unusable for many applications.

OBJECTS OF THE INVENTION

The underlying aim of the present invention is to provide a method and adevice for spreading a flat web of material (1) which is guided andtransported via rollers. The method is intended to ensure that the webof material (1) can be guided and transported without folds andelongations in the longitudinal and transverse directions. At the sametime it is of particular importance that the method can be adapted, i.e.the method should be equally successfully employed at different speedsof travel of the web of material (1) and for different materials. Inaddition the device should require low maintenance and have little needfor repair.

SUMMARY OF THE INVENTION

This task is solved by a method for guiding a flat web of material (1)in which the web of material (1) runs in an arrangement of rotatingrollers at a web speed v_(F) and the web of material (1) is guided inboth peripheral regions via at least one spreader roll (2) whichproduces a tensile stress in the transverse direction, i.e. crosswiserelative to the direction of travel of the web of material (1), whereinthis tension in the transverse direction is controlled by closed-loopcontrol of the circumferential speed v_(R) of the spreader roll (2)and/or by open-loop control of the angle and/or the contact surface area(3) between the surface of the roll (5) and the web of material (1) andwherein the circumferential speed of the spreader roll (2) v_(R) isgreater than the web speed v_(F).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross-sectional view of the spreader roll (2),b_(g) being the overall width of the spreader roll (2) and b_(M) beingthe hub face of the roll.

FIG. 1a shows a particular embodiment of the spreader roll (2) likewisein schematic cross-sectional view in which the surface of the roll (5)is not chamfered and is, accordingly, particularly wide.

FIG. 2 shows the spreader roll (2) in side elevation.

FIG. 3 shows the spreader roll (2) from FIG. 1 in perspective view.

FIG. 3a shows the spreader roll (2) from FIG. 1a in perspective view.

FIG. 4 illustrates the contact surface (3) of the spreader roll (2) onthe web of material (1).

FIG. 5 is a schematic illustration of the positional possibilities ofthe spreader rolls (2) as a function of the angle a to the web ofmaterial (1). V_(F) represents the web speed and the arrow specifies thedirection of travel of the web of material (1).

FIG. 6 is a schematic illustration in side elevation of the web ofmaterial (1) which is guided via the spreader roll (2). The angle βresults from the point of incidence p of the web of material (1) on thespreader roll (2) and the backward extrapolation shown by a dotted lineof the web of material (1) behind the spreader roll (2). The depth ofinsertion of the spreader roll (2) into the web of material (1) isdesignated by h. The direction of rotation of the spreader roll (2) andthe direction of travel of the web of material (1) are indicated by thearrows. V_(R) and V_(F) respectively designate their speeds.

FIG. 7 is a perspective illustration of the positioning of the spreaderrolls (2) relative to the web of material (1) as a function of the angleα. The arrangement of the discharge electrodes (4) is also sketched in.

DETAILED DESCRIPTION OF THE INVENTION

The longitudinal direction as defined in the present invention is thedirection in which the web of material (1) runs; this direction is alsoreferred to as the machine direction. As defined in the presentinvention the transverse direction is that direction running at an angleof 90°, i.e. crosswise, to the machine direction.

In the production and processing of flat webs of material these webs areguided in an arrangement of rotating rollers. The circumferential speedsof the individual rollers are controlled and determine, on the one hand,the speed at which the web runs and, on the other hand, the differentroller speeds also predetermine a tension which is introduced in thelongitudinal direction of the web of material. This tension in thelongitudinal direction is necessary in order to ensure undisturbedpassage of the web of material over the rollers and the downstreamdevices integrated in the roller arrangement such as thickness gauges,corona station or the like.

The method according to the invention overcomes the disadvantages whicharise due to the tension introduced in the longitudinal direction. Themethod is suitable for various flat webs of material and canadvantageously be employed in all cases in which fold formation orshifts occur in the longitudinal direction of the web of material whenguided over and between rotating rollers. The method has proved to beeffective in particular for films made from plastics, in particularthermoplastics. Films made from thermoplastic materials include forexample films made from polyester and polyolefins, such aspolyethylenes, polypropylenes and cycloolefins, polycarbonate,polyamides, etc. Such films can be of single-layered or multi-layeredconstruction. The method can also be applied for webs made of othermaterials, for example webs of fabric, paper or metal. The method isequally advantageous in the production of laminates or for guiding thelaminate itself. Different materials are also possible for thelaminates. The method is particularly suitable for webs of materialhaving a thickness of 0.5 to 500 μm, preferably 2 to 200 μm.

The web speed v_(F) of the web of material is determined by the targetproduction or processing speed. Depending on the type of material theusual web speeds are between 1 to 2,500 m/min, preferably 5 to 1,000m/min. For films made from thermoplastic polymers speeds of 100 to 1,000m/min are usual. On the one hand, the tension in the longitudinaldirection to be introduced into the web of material is determined by theproperties of the material (e.g. type of material) and its thickness orthe purpose of the following devices (e.g. thickness gauge, surfacetreatment, winding station) which are integrated in the rollerarrangement or arranged downstream and, on the other hand, the web speedv_(F) itself and the tension to be applied in the machine direction aremutually interdependent. Due to the air entrained by the web ofmaterial, air cushions between the roller and web of material build upahead of the rollers which must be pushed away by the tension introducedinto the web of material. The higher the web speed the more easily dounwanted air cushions form and the higher in general the tensile stressin the longitudinal direction has to be to pinch off these cushions.Thus, web speed and tension are given parameters in production orprocessing operations which can be varied only within a limited range,even when folds and shifts in the longitudinal direction occur. Theseproblems are efficiently overcome by the method according to theinvention, wherein web speed and tension can be kept within the desiredrange.

Accordingly, the method according to the invention is particularlyadvantageous for production or processing operations involving high webspeeds.

According to the invention, the web of material (1) is guided in itsperipheral region over one or more spreader rolls (2). The peripheralregion of a web of material (1) is usually narrow in relation to thetotal width of the web. The exact width of such a peripheral region willdepend on the nature of the material and the overall width of the web.Generally, a peripheral region is understood to be the outer regions ofthe web which together may account for up to 30% of the total width. Asa rule each peripheral region amounts to 1 to 10% of the total width ofthe web of material. It is a matter of course that every continuous webof material has two edges which run parallel to the machine direction.The following details about “the peripheral region” naturally apply alsoin equivalent manner to the corresponding opposite edge.

The web of material (1) is guided in the peripheral region over aspreader roll (2). This spreader roll (2) is of such a size that itsdiameter is usually greater than its width b_(g) so that the term “roll”more aptly characterizes the element than the term “roller”. It is,however, not ruled out that appropriately sized rollers may also fulfillan equivalent purpose. The person skilled in the art will select thesize of the element as a function of the web of material (1), the webspeed and the width of the peripheral region. Generally, the spreaderroll (2) has a width b_(g) of 1 to 500 mm, preferably 1 to 150 mm, andin particular 1 to 50 mm. The diameter of the spreader roll (2) isgenerally 1 to 10% of the width of the web of material (1). The width ofthe web of material depends on the type of material and the givendimensions of the machine and can, accordingly, vary over a wide range.For films made of thermoplastics, customary web widths in the productionof the film prior to transverse orientation range from 0.2 to 2 m,preferably 0.5 to 1 m, but after transverse orientation range from 0.5to 30 m, preferably 1 to 20 m. The absolute values for the roll diametermay vary correspondingly within broad limits.

In principle the spreader roll (2) can be produced from any material orcomposite material which meets the requirements. The surface should bedesigned in such a way that a non-positive connection between the web ofmaterial (1) and the surface of the roll (5) is promoted. In aparticular embodiment it is necessary to ground the surface electricallyto zero potential.

In a preferred embodiment the roll is beveled or chamfered at the edgesin such a way that the hub face b_(M) becomes narrower so that thecontact surface area (3) between the web of material (1) and the surfaceof the roll (5) is reduced in the ideal case to a point or a line. Ingeneral, the hub face b_(M) in beveled or chamfered embodiments willhave a width of 0 to 400 mm, preferably 1 to 200 mm. Such beveled orchamfered rolls are particularly advantageous since the relative motionbetween the hub face b_(M) and the web of material (1) becomes steadilysmaller as the hub face diminishes. In addition, beveled or chamferedrolls afford a certain degree of protection against damage to the web ofmaterial (1).

The spreader roll (2) does not necessarily require an independent drive.It can be driven by the running web of material (1) and then has acircumferential speed v_(R) which corresponds to the web speed v_(F) ofthe web of material (1) taking account of the cant angle α. In apreferred embodiment the spreader roll (2) is provided with a drivethrough which the circumferential speed of the roll V_(R) can besubjected to open-loop or closed-loop control. Spreader rolls driven inthis way are preferred. The drive allows the circumferential speed ofthe roll to be controlled in open-loop or closed-loop fashion and,moreover, allows the tension produced in the crosswise direction to becontrolled also. For driven rolls, with the cant angle α being takeninto account the circumferential speed v_(R) can be set in such a waythat the circumferential speed v_(R) is at least just as high as andpreferably greater than the web speed v_(F) of the web of material (1).The lead of the circumferential speed v_(R) of the roll is usually setin such a way that no relative motion occurs between the surface of theroll (5) and the web of material (1).

In another preferred embodiment the spreader roll (2) has anelectrically conducting surface which is grounded to an electricpotential of zero. This surface allows a particularly advantageousembodiment of the method according to the invention in which anon-positive connection between the contact surface of the spreader roll(2) and the web of material (1) is achieved by electrostatic charging ofthe web of material. This embodiment of the method is explained indetail below.

To carry out the method according to the invention the spreader rolls(2) are positioned in the two peripheral regions of the web of material(1). The position of the spreader rolls (2) on the running web ofmaterial (1) is chosen on the basis of mechanical engineering andergonomic considerations. Driven spreader rolls (2) are driven in such away that they revolve in the machine direction of the web of material(1). To position the roll in relation to the running direction of theweb a cant angle α is set (see FIG. 7). This angle must be greater than0° and less than 90°. In general, a cant angle in the range of 2 to 50°,preferably 5 to 30°, will be set. The speed of the roll v_(R) iscontrolled in open-loop or closed-loop manner by the setting of theangle. The settings chosen for the open-loop or closed-loop control ofthe individual parameters are interdependent. Thus, by way of example,the following relationship between the cant angle α to be set and thecircumferential speed of the roll v_(R):

v _(R) =v _(F): cos.α.

Thus, for a larger cant angle α a higher circumferential speed v_(R)must be selected if there is to be no relative motion between the web ofmaterial (1) and the surface of the roll (5).

Finally, the spreader rolls (2) are also positioned in the thirdpossible spatial dimension. The roll must first of all be moved farenough in the direction of the web of material (1) that the surface ofthe roll (5) plunges into the web of material (1). This positioning isalso referred to below as the depth of insertion h (see FIG. 6). Thedepths of insertion of the spreader roll (2) into the running web ofmaterial (1) determine how much the web of material (1) wraps around thespreader roll (2). The higher the wrap angle β the greater is thecontact surface area (3) produced between the surface of the roll (5)and the web of material (1).

In another particularly advantageous embodiment of the invention thenon-positive wrap around the roll is assisted by electrostatic chargingof the web of material (1). For this purpose a discharge electrode (4)is fitted in the region of the point of incidence P, viewed in themachine direction of the web of material (1), of the web of material (1)onto the spreader roll (2) (see FIGS. 6 and 7). By means of thisdischarge electrode (4) an electric charge is applied to a small regionof the web of material (1). If the web of material (1) charged in thisway then runs over an electrically conducting spreader roll (2) groundedto an electric potential of zero the web of material (1) is attracted bythe surface of the spreader roll (5). This results in a particularlygood non-positive connection between the web of material (1) and thecontact surface (3) and possibly also in a larger wrap angle β. In thisway the person skilled in the art is furnished with a further parameterthrough which (s)he can regulate the force acting in the transversedirection. The higher the charge voltage the greater is the contactforce and possibly the wrap angle β, due to which in the final analysisany potential slippage between the web of material (1) and the contactsurface (3) is eliminated and a transverse force can be built up byadvancing the speed of the spreader roll (2).

The invention opens up a simple way of introducing a tensile stress inthe crosswise direction of a continuous web of material. This method isparticularly advantageous since it affords various possibilities forcontrolling this tension in the transverse direction. The tensile stresscan be controlled by varying the diameter of the roll, by means of thecant angle α, by means of the depth of insertion h, by means of thedesign of the surface of the roll, by means of the circumferentialspeed, by means of the positioning of the spreader roll relative to theweb of material and by means of the static charge. In this way it ispossible to very finely adjust the forces acting in the transversedirection via different presettings. The method according to theinvention is extremely flexible and can be used advantageously for themost varied materials and production or processing methods. It allowswebs of material to be guided without folds through rotating rollers anda controlled tension to be built up in the transverse direction so thatshifts or other faults which may arise due to the tensions in thelongitudinal direction are reliably prevented.

What is claimed is:
 1. A method for guiding a flat web of material (1)in which the web of material (1) runs in a machine direction in anarrangement of rotating rollers at a web speed v_(F), comprising thestep of: guiding the web of material (1) in its peripheral region with aspreader roll (2) which produces a tensile stress in a transversedirection which is crosswise relative to the machine direction of theweb of material (1), wherein this tensile stress in the transversedirection is controlled by at least one of a closed-loop control of acircumferential speed v_(R) of the spreader roll (2), an open-loopcontrol of a cant angle α of the spreader roll (2) relative to themachine direction, and an open-loop control of a wrap angle β of the webof material (1) on the spreader roll (2), and wherein thecircumferential speed v_(R) is greater than the web speed v_(F).
 2. Themethod according to claim 1, wherein the web of material (1) is a web ofmaterial composed of a material selected from the group consisting ofthermoplastic, polyester, polyethylene, polycarbonate, polypropylene,and cycloolefin polymer.
 3. A method according to claim 1, wherein theweb of material (1) has a thickness of 0.5 to 500 μm.
 4. A methodaccording to claim 3, wherein the web of material (1) has a thickness of2 to 200 μm.
 5. A method according to claim 1, wherein the web speedv_(F) of the web of material (1) is 1 to 2,000 m/min.
 6. A methodaccording to claim 1, wherein the peripheral region of the web ofmaterial (1) is 1 to 10% of a total width of the web of material (1). 7.A method according to claim 1, wherein the spreader roll (2) has adiameter in a range of 1 to 500 mm, and wherein the diameter of thespreader roll (2) is greater than a width of the spreader roll (2).
 8. Amethod according to claim 1, wherein the spreader roll (2) has a surface(5) selected from the group consisting of a metallic surface and aconductive surface, and wherein the surface is grounded to an electricpotential of zero.
 9. A method according to claim 1, wherein thespreader roll (2) has beveled edges.
 10. A method according to claim 1,wherein the spreader roll (2) is connected to a drive which controls thecircumferential speed v_(R) of the spreader roll (2).
 11. A methodaccording to claim 1, wherein at least two spreader rolls (2) arepositioned adjacent a pair of opposite peripheral regions of the web ofmaterial (1) and form a cant angle α relative to the machine directionof the web of material (1) that is greater than 0° and less than 90°.12. A method according to claim 11, wherein said cant angle α of thespreader rolls (2) relative to the machine direction is within a rangeof 2 to 50°.
 13. A method according to claim 1, wherein the spreaderroll (2) is engaged with the web of material (1) such that the web ofmaterial (1) partially wraps around the spreader roll (2).
 14. A methodaccording to claim 13, wherein the web of material (1) engages thespreader roll at a point of incidence (P), wherein the spreader roll (2)has a conductive surface (5), and wherein a discharge electrode locatedadjacent the point of incidence (P) applies a charge to the web ofmaterial (1).
 15. A method according to claim 2, wherein the web ofmaterial (1) has a thickness of 2 to 200 μm, wherein the web speed v_(F)of the web of material (1) is 1 to 2,000 m/min, wherein the peripheralregion of the web of material (1) is 1 to 10% of a total width of theweb of material (1), wherein the spreader roll (2) has a diameter in arange of 1 to 500 mm, and wherein the diameter of the spreader roll (2)is greater than a width of the spreader roll (2).
 16. A method accordingto claim 15, wherein the spreader roll (2) has a surface (5) selectedfrom the group consisting of a metallic surface and a conductivesurface, and wherein the surface is grounded to an electric potential ofzero.
 17. A method according to claim 16, wherein the spreader roll (2)has beveled edges, and wherein the spreader roll (2) is connected to adrive which controls the circumferential speed v_(R) of the spreaderroll (2).
 18. A method according to claim 17, wherein at least twospreader rolls (2) are positioned adjacent a pair of opposite peripheralregions of the web of material (1) and form a cant angle (α) relative tothe machine direction of the web of material (1) that is within a rangeof 2 to 50°.
 19. A method according to claim 18, wherein the spreaderroll (2) is engaged with the web of material (1) such that the web ofmaterial (1) partially wraps around the spreader roll (2).
 20. A methodaccording to claim 19, wherein the web of material (1) engages thespreader roll at a point of incidence (P), wherein the spreader roll (2)has a conductive surface (5), and wherein a discharge electrode locatedadjacent the point of incidence (P) applies a charge to the web ofmaterial (1).